1. Field of the Invention:
This invention relates to the outline image forming method which constitutes one of image forming processes relying upon the electrophotographic copying technology. More specifically, it relates to a method for the formation of outline images corresponding to peripheral outlines of negative document's images or negative images formed by laser, LED and the like.
2. Description of the Prior Art:
Generally speaking, the peripheral outline of an image is in practice full of necessary information thereabout and represents enough sufficiently the characterizing features of the given image, thus playing among others a most important role in the judgement of the latter.
The outline image so-called means such that a peripheral outline is picked up from an image and devoid of intermediate tones of reversely, solid representations, thus being most effective for the identification of the practical image and for pattern recognization purpose thereof.
As an example, such a complex color image pattern may be attractive to realize by execution of twice successive copying operations a blank pattern encircled by a color outline, or to prepare a blank pattern for later producing differently colored local image areas contained therein.
It should be noted that in the name of the present assignee company per se, it has already been proposed to realize an outline image-forming process, wherein, in case of the mono-component type toner developing method using conductive toner to develop static latent images, said process being characterized by that, between the material to be subjected to developing and the carrier for the conductive toner, a d.c.-bias voltage is impressed at a medium potential ranged between maximum and minimum surface potential of said material and having an opposite polarity to the static latent image charge, for extracting the outline marginal configuration only from the latent image on said material to be developed (refer to Japanese Open Patent Specification, unexamined, Sho-51-134635).
It should be further noted, however, that there is a considerable drawback in the above-mentioned prior art improvement. In this proposed process, indeed, the developed marginal outline image is only of negative one, because of such fact that the marginal outline of the static latent image is also negative and the conductive toner will be deposited onto substantial part of the latent image devoid of the marginal outline thereof, and indeed, by virtue of higher potential difference charged at the substantive part of the latent image on the drum. In practice, however, the wanted marginal outline should preferably be in black and thus positive. Therefore, the thus formed negative outline image must generally be subjected to a further reproducing step relying upon the reverse development principle, which represents naturally a grave and troublesome drawback inherent in the above improving known process.